1. Field of the Invention
The present invention relates to an imaging apparatus, and, more particularly, to a printhead gap adjustment mechanism for an imaging apparatus.
2. Description of the Related Art
A typical imaging apparatus, such as an ink jet printer or a thermal printer, forms an image onto a recording medium, such as paper or film, by causing ink or the like to be deposited onto the recording medium. For example, an ink jet printer forms an image on a recording medium by positioning a printhead in close proximity with the recording medium, and selectively ejecting ink from a plurality of ink jetting nozzles of the printhead to form a pattern of ink dots on the recording medium.
During ink jet printing, the printhead is spaced apart from the recording medium in a plane perpendicular to the recording medium. As the printhead is moved across the recording medium, from one end to another in a scan direction, ink is selectively ejected from the ink jetting nozzles to form a print swath. After completing at least one print swath, the recording medium is indexed a selected amount in a sub scan, i.e., paper feed, direction.
During the printing operations, the printhead must maintain a certain spacing, or gap, relative to the recording medium. Various factors affect the size of the gap, including tolerance stack up of manufactured parts, intentional or unintentional variation in recording medium thickness or weight, ambient thermal and humidity conditions, and settling or shifting of printer components due to shipping and setup at the user premises.
Analyses have shown a correlation between print quality and the printhead gap, i.e., the distance from the ink jet printhead to the recording medium. It is known in the art to provide printhead gap adjustment. For example, one conventional design employs a two-stage carrier lift mechanism, wherein the printhead location may be changed by moving a positioning lever. Such designs typically rotate the carrier shaft on an internal eccentric. Another design employs the use of a link and cam system to lift the printhead carrier. Although both of these designs provide repositioning of the printhead in a printhead gap direction, they typically provide two distinct positions, and they also yield printhead movement in directions other than the printhead gap adjustment direction.
What is needed in the art is an improved printhead gap adjustment mechanism for use with an imaging apparatus.
The present invention provides an improved printhead gap adjustment mechanism for use with an imaging apparatus.
In one form thereof, the present invention relates to a printhead gap adjustment mechanism for use in an imaging apparatus. The imaging apparatus includes a printhead carrier that carriers a printhead, a frame, and a carrier shaft. The carrier shaft is rotably and slidably coupled with the printhead carrier and the frame. The printhead gap adjustment mechanism includes a worm gear coupled to the carrier shaft to transmit a rotational motion to the carrier shaft. A worm screw is positioned in rotational cooperation with the worm gear, the worm screw having an axis of rotation. A first cam is coupled to the carrier shaft. A first cam follower surface is disposed in proximity to the first cam. A guide device guides the carrier shaft in a translational direction substantially parallel to the axis of rotation of the worm screw. A rotation of the worm screw transmits rotational motion to drive the first cam via the worm gear and the carrier shaft. The first cam engages the first cam follower surface to effect a translational motion of the worm gear in the translational direction, thereby effecting a movement of the printhead in the translational direction.
An advantage of the present invention is the ability to adjust the printhead position in the direction of opening or closing the printhead gap, i.e., a printhead gap adjustment direction, without the adjustment having any effect on the printhead location other than perpendicular to the recording medium.
Another advantage is to provide the capability of infinite adjustment of the printhead gap within a given pre-selected range.
Yet another advantage is to provide the capability to make printhead gap adjustments using a low-cost unidirectional motor.